The present invention relates to the general classification of archery bows, and more particularly to cross bows and vertical bows operated with draw-locking and release features.
Bow hunters strive for high speed/flat trajectory and deep penetration energy when using either compound bows or crossbows, but each type of bow produces its arrow's flight energy in a different manner. A compound bow typically has a lower maximum draw weight (e.g., 50-80 lbs, with a 50% or greater drop-off at full draw), but a longer power stroke (e.g. 18-24 inches) than the crossbow—which by comparison typically has a high draw weight (150-225 lbs) but a short power stroke (10-14 inches). These differences produce commensurate differences in arrow/bolt speed and penetration. For example, a 70 lb pull compound bow will typically launch an arrow at a higher velocity than a 150 lb crossbow does with its shorter and lighter bolt.
Power stroke is the distance the bow string travels from full draw to the rest position. For example, a compound bow with a 30 inch draw length and a 7 inch brace height (distance from grip to the string at rest) has a 23 inch power stroke (30−7+23). A person using a 30 inch draw will shoot the same weight arrow faster than one using the same draw weight and arrow with a 28 inch power stroke. The same relationship exists with the crossbow—longer power stroke causes higher velocity.
The power stroke and draw weight variations have other effects beyond speed and energy. The most noticeable effect of the draw weight is the effort and techniques used to draw the bow. The heavy draw weight of the cross bow usually requires two-handed cocking using leg and back muscles to draw the string against a foot stirrup or bar. Some archers may not have enough strength for even that two-handed maneuver, and must rely upon a mechanical crank. This effectively limits a crossbow hunter to a single shot at game, since it is cumbersome to re-cock the cross bow and nock a bolt in a tree stand or cramped blind. On the other hand, a hunter can hold the loaded crossbow on an approaching target for an extended time while waiting for the range and cover to present an opportunity for a lethal shot, since there is no draw weight acting against the archer's muscles. De-cocking the crossbow is another difficult task, and many find it more convenient to simply fire the bolt into soft ground to de-cock.
The compound bow is the more accurate weapon in the hands of an experienced archer because of its consistent anchoring point when using string loop and mechanical release, which defines the nock point more consistently than does the crossbow latch, but the crossbow allows much faster mastery by beginners, as its aiming and trigger systems closely resemble a shoulder mounted firearm. The crossbow is also heavier than a compound bow, and less maneuverable in brush or tree branches.
Considering that the main advantage of the crossbow is its ability to draw and lock it at full draw until ready to shoot, it is not surprising that innovators have devised mechanisms to lock a compound bow at full draw. A representative example of these draw-locking mechanisms is shown in U.S. Pat. No. 5,671,723 by the present inventor.